Fuel system for gas turbine engines having means for avoiding compressor instability



Aug. 12, 2,846,846

FUEL SYSTEM FOR GAs TURBINE ENGINES HAVING MEANS 1958 F. c. MocK FoaAvoIDING COMPRESSOR INSTABILITY 3 Sheets-Sheet 1 Fil'ed June 14, 1951 46 W7 wea-.A

F v I INVENTOR. '15E FwA/A/I/Vafv/f.

Aug. 12, 1958 F. c. MocK 2,846,846

FUEL SYSTEM FOR GAS TURBINE ENGINES HAVING MEANS FOR AVOIDING COMPRESSORINSTABILITY Filed June 14. 1951 5 Sheets-Sheet 2 N INVENToR.

Aug.. 12, 195s Filed June 14. 1951 F. c. MocK 2,846,846 FUEL sySTEMEoRGAS TUREINE ENGINES HAVING MEANS FOR AvoInING COMPRESSOR INSTAEILITY 5Sheets-Sheet 3 United States Patent O FUEL SYSTEM FOR GAS- TURBINEENGINES HAV"- ING MEANS FOR AVOIDING` COMPRESSOR INi- STABILITY Frank C.Mock, South Bend, Ind., assigner to. Bendix Aviation Corporation, SouthBend, Ind., a corporation of Delaware Application June 14, 1951, SerialNo. 231,556`

16 Claims. (Cl. 611-3928) This invention relates to a fuel feed and`power control system for gas turbine engines; more particularly for gasturbine engines adapted for the propulsion of aircraft, such as what arenow commonly known as turbojet and turboprop engines.

It is, of course, highly desirable that a pilot or operator of aturbojet or turboprop engine be free to accelerate rapidly and smoothlyat all altitudes simply by resetting a control lever or member to 'aselected power position without worrying about, or danger of, (a)exceeding the upper temperature limit for that particular engine, (b)causing ame blow-out in the burner or burners, or (c) producing surge orcompressor stall, and which latter in a turboprop engine may also occuras a result of decreasing speed upon application of an external load..Another transitional hazard that should be mentioned is flame-out orburner die-out upon deceleration or sudden closure of the throttle andreduction in fuel feed .at vhigh engine speed.

With a dynamic air compressor running at agiven speed and deliveringthrough an orifice of fixed size, the air weight delivery tends to varyas the entering pressure and inversely as the entering temperature. lfthe air be raised in temperature vafter leaving the compressor butbefore reaching 'the discharge orifice, this will in general cause theweight delivery to ldecrease and the delivery pressure to rise, up to apoint where'the compressor stalls. If, however, the delivery conditionsbe such that the velocity of flow through the orifice approximates thatof sound, as indicated or defined by the absolute temperature of the airapproaching the orifice, this absolutely limits the weight flow throughthe orifice; the velocity varies with the square root of the absolutetemperature, and the density inversely as the absolute temperature (anddirectly with the pressure), so that the net weight ow varies with thesquare root of the absolute temperature.

This latter is generally the case with a gas turbine in the maximumpower range. The velocity is sonic through the nozzles through which thegas enters the turbine blades; the Weight ow varies with the square rootof the yentering gas temperature and 'directly with its pressure; andall this is lonly remotely connected with the temperature entering thecompressor.

If the weight of air passed by the Aturbine under the .condition ofmaximum turbine gas temperature, which is as above stated practicallyindependent of entering'air temperature, is in excess of that quantitywhich the compressor could deliver at the vsame pressure (note that thislast quantity does vary with .entering air temperature), the turbine gastemperature dictates the maximum amount of fuel which can be fed. But ifraising the turbine gas temperature to the maximum indicated by turbineendurance causes the compressor'to stall, 'then lower combustiontemperature, lower fuel ilow, and lower thrust must be tolerated.Obviously, 'the engine design must be such as to permit 'the engine tolrun at steady 2,846,846 Patented Aug. 12, 1958 ice 2 speed withoutcompressor stall; andthe loss-in perform,- ancerimposed by compressorstall characterlstics 1s-y usually confined to slower acceleration inthe mid-speed range.

In illustration of the foregoing, the fuel feed requirementsfof a givenaxial compressor type turboJet engine in the. higher compression ratiosat constant entering air pressure (given altitude)l but at varying ortwo differ ent-entering air temperatures are assumedY to be;v as plottedin-thecurve chart of Figure l, wherethefull linesrepresent therequirements for a warm entering air. temperature, say in theneighborhood of F., and the dotted. lines a cold` entering airtemperature, for instance -10 F. Here the lines EA,.EA1 indicate themaximum rate of fuel feed to be observed in orden to keep within at.safe. upper turbine. temperaturelimit, and they also indicate, a trendwhich will avoid blow-outfparticularly at altitude. The curved lines DBand D1B1 define the surge area; they indicate the rate of fuel feed to be observed to avoid surge, or the upper limit on the rate of fuel feedas determined by the surge. characteristic of that particular engine.The curves YX and YlXl represent the rates. of fuel feed required tomaintain a steady speed; with an all-speedl governor` type4 throttlevalve they represent xed throttley settings. at an equilibrium orbalanced condition with respect to the rate of fuel feed.v and enginespeed.

In Figure 2 an attempt is madeI to approximate the quantity of fuelrequired to maintaina l600= F; turbine inlet temperature for fou-rdifferent sets of entering air pressure and temperature values showingthe relationship of fuel feed rate to compressor rise.

The relations of required fuel ilow, engine speed, entering air andturbine gas temperatures, combustion ethciency, and compressor stall areboth mathematically complex in theory and functionally irregular inpractice. l have. found, however, that the following more or lessempirical relations give a close enough approximation to permit animproved and practical scheme of control. In the following, the symbolsP1 and T1 designate, respectively, the. pressure and temperature of theair entering the compressor; P2, the pressure just beyond thecompressor; and T3, the temperature of the gas entering the turbine.Note that the limiting values of fuel feed given vary according to theconsecutive listed conditions of engine operation:

(l) With a given absolute safe value of T3, turbine gas temperature, theamount of fuel that can be tolerated per pound of air will decrease withincrease of T1, entering air temperature, or with increase ofcompression temperature. I have found that to hold a given turbine gastemperature under changes of entering air temperature and pressure, thefuel feed should Hvary vgenerally as .maximum engine speed under .changeof entering air pressure and temperature lies between (l) and (2) above.

But when a governor is used to determine maximum speed, as in theinvention here described, ,no particular correction is needed providedthe maximum scheduled fuel feed is in excess of that required for steadyoperation at maximum speed. While compressor pressure rise haspreviously been proposed as a means of fuel metering, it is believedthat the exponential values of pressure and temperature compensation, asherein set forth, are novel, distinctive and valuable in the art. Themechanical adaptation shown also presents the advantage of beingstraightforward, simple and capable of rather general application withminor change. Another novel element of the invention is a so-called-stall modulator construction by a variable orice in series with themain governor metering orifice. This provides both automatic temperaturecompensation for the stall range and also forms a manual adjustment forminor variations between engines of the same model. Its action is alsosimple and straightforward.

In the drawings:

Figures 1 and 2 are curve charts for supplementing thebrief analysis ofthe theory on which the invention is based;

Figure 3 illustrates schematically one form of fuel feed and powercontrol device capable of functioning in accordance with the invention;

' Figure 3A is an enlarged longitudinal section of a temperaturecompensating control valve; and

Figure 4 is a performance curve for an engine equipped with the improvedcontrol.

Referring to Figure 3 in detail, a gas turbine engine is generallyindicated at 19 which includes a series of combustion chambers 11,mounted in a casing having a header or air intake section 12. A dynamiccompressor is indicated at 13 and is shown as of the axial fiow typedriven by Vmeans of a turbine 14 through a shaft 15. Each of thecombustion chambers is provided with a burner nozzle 16 to which meteredfuel is supplied under pressureby way of a conduit 17, fuel manifold 18,and'individual fuel lines 19, in a manner to be described.

The parts which go to make up the fuel metering and power control systemmay be classified generally as a metering head regulator section 21,governor section 22, and stall modulator section 23.

Fuel from a suitable source of supply, such as a fuel tank, not shown,flows to the regulator through inlet conduit 24, having a suitablepressurizing device therein, such as a pump 25 of the by-pass type whichmaintains the supply at a substantially constant pressure. From conduit24 the fuel flows through ports 26 and across regulator valve 27 tochamber 28. Valve 27 is preferably of the balanced type and iscontrolled by a double or dual regulator comprising a pair of diaphragms29 and 30, the diaphragm 29 constituting a movable wall betweenexpansible chambers 28 and 31 and the diaphragm 30 a like wall betweenexpansible chambers 32 and 33. Chamber 31 is vented to metered fuelpressure by way of passage 34, chamber 32 to compressor inlet or P1pressure by way of passages 35 and 36, and chamber 33 to compressoroutlet or P2 by way of passage 37, variable orifice 38 and passage 37.The area of orifice 38 is controlled by a contoured needle valve 39,carried by the movable end of a pressure responsive bellows 40, mountedin a chamber 41, which is vented to compressor inlet or P1 pressure byway of passage 35. Between chambers 33 and 32 is a passage 42, havingtherein a variable orifice 43, the area of which` is controlled by acontoured needle valve 44, carried by the movable end ofl a temperatureresponsive bellows 45 connected by capillary tube 46 with a temperaturebulb 47, located to sense compressor inlet or entering air (T1)temperature.

As will be more fully explained in the description of operation, theeffective fiow position of the regulator valve 27 and hence the meteringhead between chamber 28 and fuel conduit 17 is determined by thedifferentials `across diaphragms 29 and 30'. The forces (pressuredifference times area) at a given pressure drop between chamber 28 andmetered fuel conduit 17 and at a given compressor rise and entering airpressure and temperature, will be equal and opposite, or their sum totalwill be zero, and balanced valve 27 will remain at a given flowposition; but should there be a change in any of these variables andhence in any one of botn =of the said differentials, the regulator willbecome unbalanced and valve 27 will be repositioned to increase ordecrease the pressure in chamber 28 until a balanced condition is againestablished. Since the flow through a metering orifice tends to vary asthe square root of the metering head, the quantity of fuel metered tothe engine will be proportionate to the square root of the compressorrise modified by entering air pressure and temperature.

From chamber 28, fuel fiows to the outlet conduit 17 through passage 48,either one or both orifices 49 and Sii, chamber 51 and metering orifice52.

The area of the metering orifice 52 is controlled by an all-speedgovernor valve 53, which is preferably of the balanced type and isslidably mounted in a seat or sleeve 54. The valve 53 is provided with aheaded stem 55 engaged by a governor spring 56 adapted to be variablytensioned by a lever 57 which constitutes a power control member (or maybe connected to such member), said spring tending to open the valve 53against the balancing force of governor weights 58, pivotally mounted onbrackets 59, carried ny rotatable gear 60, formed on the inner end of ashaft 61. The gear 6l) is driven in relation to engine speed from ashaft 62 and gear 63. The maximum opening travel of governor valve 53 isdetermined by a stop 64 externally adjustable by means of screw 65,while its minimum closing travel may be determined by adjustable guiderod 64.

To 4select a desired engine speed, the pilot or power control lever 57is reset to a position which will subject governor spring 56 to a givencompression or tensioning action which will unbalance the then existingequilibrium condition of the governor weights 5S with respect to thegovernor spring, whereupon the throttle or governor valve 53 will eitheropen or close to increase or decrease flow of fuel to the engine and thespeed of the latter will either increase or decrease until anequilibrium condition is again attained as determined by the setting ofthe pilots control lever. Also, at a given setting of the pilots controllever, should be the speed of the engine tend to vary from the selectedspeed, the governor will become unbalanced, whereupon the governorweights will automatically adjust valve 53 to return the engine speed tothe selected value, as is well understood by those having a knowledge ofthe art. Should the pilot reset his control lever to accelerate to fullpower from a low or intermediate power setting, valve 53 would open to amaximum as determined by stop 64 and the engine would accelerate tomaximum governed speed with the rate of fuel feed at each point oftransition determined by the metering area of orifice 52 and the fuel ormetering head across said orifice. As heretofore noted, the meteringhead across orifice 52 is a function of compressor rise and entering airpressure and temperature; and it is further subject to modificationduring part of the speed range by the stall modulator system in section23, to obtain the dip BCD or BICD, in Figure l.

Referring to the modulator section 23 of Figure 3, the variable orifice49 is regulated by a contoured valve 70 which is positionedautomatically as a function of engine speed by a speed-sensing elementgenerally indicated at 71 and comprising centrifugal weights 71' whichare pivotally mounted on brackets 72 carried by the gear 63 and havinginner fingers or shoes engaging a collar or bearing surface 73 on theadjacent end of a shaft or rod 74, said rod being slidably mounted in abushing` 75 and having its opposite end provided with spaced collars 76between which the adjacent or upper forked end of a lever '77 engages.The lever 77 is pivotally mounted or fulcrumed at 78, and at itsopposite or lower forked end engages a pair of spaced collars or bosses79 formed on quired. A light stabilizing spring 83 may be provided forthe valve 70.

It has been found that on different engines of the same, model or design(and supposedly having the same operational characteristics) themagnitude of the stall dip or curve BCD, BlCDl with respect to fuelrequirements may be different, while the respective speeds at whichdeviation from the line AE, A1B takes place or is required may notchange. A convenient adjustment for adapting the control to suchvariations is provided by the contoured valve 85, which regulates thearea of the orifice 50 and is externally adjustable by screw 86.

As will be more fully explained in the description of operation, at somepredetermined point in the mid-speed"- range of the engine, dependingupon the setting of governor 71 by spring 81 and/or the contour of valve70, the latter becomes effective to reduce the metering head across thegovernor valve 53; and by predetermining the vfixed area of orifice 50with respect to variable parallel orifice 49, the magnitude of curvesBCD or BlCDl may be varied without varying the point of departure (speedfunction) from lines AE or A1B. This results from the fact that themagnitude of the stall fuel head varies as,

the total combined area of the orifices 49 and 50, while the particularengine speed at which the stall head starts depends upon the beginningof the .restricting action'by valve 70. In this connection it will beunderstood that .the total or combined area of parallel orifices 49and,r

50V is substantially in excess of the area of the metering orifice 52.

The temperature modifying action on the fuel head by valve 44 isproportionately effective throughout the range of engine speed, but suchmodication inthe mid-..

speed range may constitute a variable; usually less tem-` peraturemodification in the surge area or mid-speed range being required. Thiscompensation is provided for by the valve unit or yassembly generallyindicated at 87, which may be used in conjunction with or substitutedfor the valve 85. An orce 88, Figure 3A, in parallel With orifice 49and/ or orifice 50, is regulated by a valve 89 having its stem slidablein bushing 90 and connected to the free or movable end of a bellows 91,in lluid communication by way of capillary tube 92 with a temperaturebulb 93, so located as to sense compressor or en-l gine inlettemperature, the lbellows, tube and bulb being loaded with a suitabletemperature responsive iiuid or gas. A spring 94 tends to urge valve 89to closed position.

It may be assumed that the control is set or calibrated-' for arelatively warm atmospheric condition at sea level (warm day), -thenshould the entering air becomeA appreciably colder, bellows 45 willshrink and produce an increase in the metering head across orifice 52.Simultaneously, however, the bellows 91 shrinks and valve 8927 reducesthe area of orifice 88, thereby reducing the total flow area provided byparallel orifices 49 and 88 and proportionally reducing the meteringhead across orifice 52. By properly contouring valves and 89, thecompensating action may be restricted to the stall range. Itiv will benoted that the contour o-f valve 70 is such that at the upper and lowerends of the speed range BA and ED, the area of orifice 49 is so great asto constitute no appreciable restriction to fuel flow, so that theposition of valve 89 at this time has little effect on the meteringvhead.

Operation In the respective positions of the vvarious parts `as shown inFigure 3, lthe engine may bel assumed to be 'operatingv at a steadyspeed in the low speed range, say at point in Figure 4. If now the pilotdesires to accelerate from 95 to 98, lever 57 would be rotatedcounterclockwise and governor valve 53 opened to the limit determined bystop 64. The suddenly increased metering area of orice 52 would resultin a sharp increase of the rate of fuel feed to, for example, point 96,but at this point the metering head takes effect and causes fuel flow tofollow the arrows to point 97 where the al1-speed governor begins to cutolf fuel and flow decreases to point 98..

When the throttle is suddenly opened, there is a momentary drop inpressure in chamber- 28 and the decreased differential across diaphragm29 will tend to open the regulator valve 27. The extent to which thisvalve opens, however, is also controlled :by the relative pressures inchambers 32 and 33, or the differential across diaphragm 30, which is afunction of compressor rise and compressor inlet pressure andtemperature. As the speed of the engine begins to increase and the riseacross the compressor increases, the differential across diaphragm 30acts in a direction to open the regulator valve 27, but this openingtravel and hence the increase in metering head is proportional tocompressor rise modified by inlet pressure and temperature, and hencethe rate of fuel feed is maintained within a predetermined upper limitand follows the arrows from 96 to 96' in Figure 4. At this point thestall modulator governor 71 has moved valve 70 to the right to where itbegins to restrict orifice 49 and reduce the fuel metering head acrossvalve 53, whereupon the rate of fuel feed is reduced to avoid the surgearea. At the lowest point in the surge dip, the maximum diameter ofvalve 70 is interposing a maximum restriction to flow through orifice49, and as said valvev moves further to the right, flow through saidorifice, `and hence the metering head across valve 53, graduallyincreases to where the rate of fuel feed again reaches the upper limitfor acceleration as it passes the surge area, at which time valve 70will have opened orifice 49 to its maximum area or to where it has noappreciable effect on said metering lhead. As acceleration continuesalong the upper temperature limit, the metering head again becomessolely a function of compressor rise, modified by compressor inletpressure and temperature. At point 97, the speed of the engine hassubstantially attained the selected value, or to where the all-speedgovernor weights 58 are substantially in 'balance with the setting ofthe governor spring 56, whereupon the rate of fuel feed decreases to thepoint 98 along the steady speed curve.

Should the pilot wish to decelerate from point 98 back to point 95,power control lever 57 is rotated clockwise, thereby relieving thetension on governor spring 56', whereupon the governor weights 58 closevalve 53 to where it is brought up against the adjacent end of guide`rod 64', and the rate of fuel feed decreases sharply to point 99,whereupon the metering head takes effect and the rate of fuel feedgradually reduces along with the compr-essor rise, until at point 10i)the all-speed governor weights 5S are substantially in balance with thesetting of the governor spring 56, whereupon fuel feed increasesslightly to point 95 along the steady speed curve.

An attempt to brieliy explain the operation of the regulator 21 follows:

First considering the fuel or hydraulic section comprising chambers 2Sand 31 and diaphragm 29, it will be seen that at a given or fixed areaof the metering restriction 52 and a given drop from chamber 28 tometered fuel conduit 17, the pressure differential between chambers 28and 31, or between passage 4S a'nd conduit 17, equals or is proportionalto the compensated pressure differential across diaphragm 30. Should themetering area of either orifice 49 or 52 be increased or decreased,there will be a momentary increase or decrease in pressure in chamber28, whereupon valve 27 will open or close to a new position where fuelow compensates .for the change in drop across orifice 49 or 52, at whichposition the differential across diaphragm 29 again equals thedifferential across diaphragm 30.

Considering now the compressor rise or air section of the regulator,comprising the chambers 32 and 33 and diaphragm 30, here thedifferential across the diaphragm 30 may be considered the primecontrolling factor of the regulator since any change therein willoperate to modify the differential across diaphragm 29 at any engineoperating condition. Without the pressure bellows 40 and temperaturebellows 45 and associated circuits, the differential across diaphragm 30would be proportional to compressor rise only, Pz-Pl, but said latterdifferential is biased with respect to the differential across thecompressor by the variable leak pressure and temperature orifices 38 and43, so that any change in these parameters operates to modify thedifferential across the diaphragm 30. Thus, the differential acrossdiaphragm 3i), and hence also across diaphragm 29, varies withvariations in P2 minus P1 and with P1 divided by T1, as does also themetering head; and since the flow across the metering orifice 52 tendsto vary as the square root of the metering head, the quantity of fuelmetered to the engine becomes proportional to the square root of Pltimes the square root of Pz-Pl divided by T1. Along the surge dip, thefuel feed rate is further modified as a function of engine speed byvalve 85 and/ or as a function of T1 by the temperature compensatingvalve 89, as heretofore explained.

In Figure 4, a sea level condition as regards altitude is assumed. Asaltitude is gained, pressure compensation for the rate of fuel feed ishad by the aneroid bellows 40, which acts to reduce the differentialacross regulator diaphragm 30 upon a decrease in pressure so that therespective curves of Figure 4 would swing downwardly until criticalaltitude for the particular aircraft is attained.

Although only one physical embodiment of the invention has beenschematically illustrated and described, such disclosure obviouslyconstitutes a teaching which will readily enable those skilled in theart to practice the invention and to make the required changes in formand relative arrangement of parts to adapt the improved control toengines having different characteristics.

I claim:

l. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, means for metering fuel to the engine at arate proportional to pressor discharge pressure, and T1 compressor inlettemperature, and means for modifying the effects of compressor inlettemperature on the rate of fuel feed in the intermediate speed range ofthe engine.

2. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, means for varying fuel iiow to the engine asa function of cornpressor rise modified by the temperature of the airiiowing to the compresor, and compressor stall control means in fiowcontrolling relation with said first mentioned means and responsive toan engine operating condition related to power output for substantiallyvarying the normal rate of change of fuel feed controlled by said firstmentioned means at a predetermined engine speed during an accelerationof the engine in such a manner that compressor instability is avoided`3. A system as claimed in claim 2 plus means operatively connected tosaid last mentioned means for varying the engine speed at which saidvariation in normal fuel feed rate occurs.

4. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, adjustable governor means for maintaining aselected engine speed, control means for adjusting said governor meansadapted to be reset to different positions to select an engine operatingspeed, means operable automatically as a function of compressor rise tomaintain the rate of fuel feed within predetermined limits during atransition of engine speed and means responsive to engine speed forautomatically modifying the rate of fuel feed controlled by said lattermeans during an acceleration of the engine.

5. A system for controlling the rate of fuel [feed to a gas turbineengine having a compressor, adjustable governor means for maintaining aselected engine speed, means in flow controlling relation with saidgovernor means and operable automatically as a function of compressorrise modified by compressor inlet temperature to maintain the rate offuel feed within predetermined limits during a transition of enginespeed, means in flow controlling relation with said last mentioned meansfor automatically modifying the rate of fuel feed as a function ofengine speed during an acceleration of the engine, and means forautomatically reducing the effects of compressor inlet temperaturecompensation during acceleration of the engine, whereby the engine maybe accelerated without encountering compressor instability.

6. In a system for controlling the rate of fuel feed to a gas turbineengine having a. compressor, the combination of a fuel metering valve,means responsive to a pressure generated by the compressor forcontrolling the fuel metering head across said metering valve, meansresponsive to a variable quantity related to power o utput of saidengine for automatically modifying said fuel metering head during anacceleration of the engine to avoid compressor instability, and meansresponsive to the temperature of the air iiowing to the compressor formodifying the pressure to which said fuel metering head controllingmeans responds.

7. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, a metering valve, means for selectivelypositioning said valve to control the metering area, a regulator valvefor controlling the fuel metering head across said metering area, meansfor automatically positioning said regulator valve as a function ofcompressor rise modified by compressor inlet pressure, and meansresponsive to changes in engine speed for automatically modifying saidfuel metering head at a preselected point in the midspeed range of theengine to avoid compressor instability.

8. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, a fuel conduit having a metering orificetherein, means for varying the area of said orifice to select an enginespeed, a regulator valve in said conduit in series wit-l1 said meteringorifice for controlling the metering head across said orifice, pressureresponsive means connected to said regulator valve, means for subjectingsaid pressure responsive means to compressor pressure rise modified bycompressor inlet pressure and temperature, a compressor stall modulatorvalve also in series with said metering Iorifice and movable todifferent positions to modify the metering head, engine speed responsivemeans for controlling said latter valve, another valve in parallel withsaid stall modulator valve, and means responsive to changes incompressor inlet temperature for controlling said latter valve, wherebyfuel flow to the engine is controlled during an acceleration thereof toavoid compressor stall.

9. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, a fuel conduit having a metering restrictiontherein, a metering valve and associated all-speed governor for varyingthe area of said restriction to select an operating speed for theengine, valve means for varying the fuel metering head across saidrestriction, means for sensing the pressure rise across the compressor,means for sensing changes in compressor inlet pressure and temperature,means operatively connecting said sensing means to said valve means toeffect variation of the fuel metering head at a rate proportional to thesquare root of compressor pressure rise times a function of compressorinlet pressure modified by compressor inlet temperature, and means forautomatically 9 modifying the action of said valve means as a functionof engine speed in the intermediate speed range of the engine duringacceleration following resetting of said governor.

10. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, a fuel conduit having a metering restrictiontherein, means for varying the area of said restriction to select anoperating speed for the engine, a iirst valve in flow series with saidrestriction, a second valve in ow series with said restriction, meansfor sensing the pressure rise across the compressor, means for sensingchanges in compressor inlet pressure and temperature, means operativelyconnecting said sensing means to said rst valve to eifect variation ofthe fuel metering head at a rate proportional to the square root ofcompressor pressure rise times a function of compressor inlet pressuremodified by compressor inlet temperature, and means responsive tochanges in engine speed operatively connected to said second valve andarranged to automatically modify the fuel metering head in theintermediate speed range of the engine during acceleration to avoidcompressor instability.

11. A system as claimed in claim 10 wherein means are provided formodifying the eect of temperature compensation on the rate of fuel ow inthe intermediate speed range of the engine.

12. In a system for feeding fuel to a gas turbine engine having acompressor and a burner or generator to which air and liquid fuel issupplied under pressure, a fuel supply conduit having a meteringrestriction therein, governor means for controlling the area of saidrestriction, means for resetting said governor to accelerate anddecelerate the engine, valve means for regulating the fuel metering headacross said restriction, means for sensing changes in compressor inletpressure and temperature, means operatively connecting said sensingmeans to said valve means, second valve means responsive to enginerotational speed in flow controlling relation with said valve means, andmeans operatively connected to said second valve means for modifying theeiects of temperature compensation on the rate of fuel feed during aportion of the acceleration range to avoid compressor instability.

13. In a system for controlling the rate of fuel feed 10 to a gasturbine engine having a compressor, a conduit for conducting fuel to theengine, means for controlling the ow of fuel through said conduit at arate which is proportional to p N/P Q-P 1 times a function of P1 with anexponent between 1 and 1/2, where P1 denotes a pressure of the airflowing to the compressor, P2 denotes a pressure which is generated bythe compressor, and T1 denotes a temperature of the air owing to thecompressor,.and means for modifying the said flow of fuel during anacceleration of the engine as a function of an engine operatingcondition related to power output.

14. In a system for controlling the rate of fuel feed to a gas turbineengine having a compressor, a fuel conduit having a metering restrictiontherein, valve means responsive to an engine operating condition relatedto power output for reducing the flow area of said restriction to avoidcompressor stall during an acceleration of the engine, and meansresponsive to a pressure derived from the compressor and in owcontrolling relation to said valve means for varying the fuel ilowthrough said restriction with variations in said pressure. v

15. A system as claimed in claim 14 plus means for modifying the derivedpressure as a function of the temperature of the air flowing to thecompressor.

16. A system as claimed in claim 14 wherein said valve means responds toengine speed and said pressure is derived from the discharge side of thecompressor.

References Cited in the iile of this patent UNITED STATES PATENTS2,422,808 Stokes .Tune 24, 1947 2,474,033 Chamberlin June 21, 19492,479,813 Chamberlin Aug. 23, 1949 2,531,664 Bolt Nov. 28, 19502,705,047 Williams et al. e Mar. 29, 1955 FOREIGN PATENTS 646,780 GreatBritain Nov. 29, 1950 941.556 France July 19, 1948 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 2,846,846 August l2, 1958Frank C Mook l lt is hereby certified that error appears in the printedspecification i of the above numbered patent requiring correction andthat the said Letters l Patent should read as corrected below. v Column4, line 5, for Hone of both" read one on both n; line 44,

strike out HbeH Signed and sealed this 17th day of March 1959.,

(SEAL) Attest:

KARL H *AX-LINE ROBERT c. wATsoN Atbeetng Officer Comissioner of Patents

